Currently, the FDA-approved treatment options for an acute ischemic stroke include intravenous (IV) delivery of clot dissolving medicine and mechanical thrombectomy.
For treatment use clot dissolving medicine, the thrombolytic agent (Tissue Plasminogen Activator (t-PA)) is injected into the vasculature to dissolve blood clots that are blocking blood flow to the neurovasculature. Intravenous t-PA is currently limited in use because it must be used within a three hour window from the onset of a stroke and can result in an increased risk of bleeding. This standard of care leaves room for upgrading, lower aisle profiles and is only the appropriate approach to treatment for a limited class of individuals, groups and temporally-limited exigent cases.
The second option includes using mechanical thrombectomy devices. Such devices are designed to physically capture an embolus or clot and remove it from the blocked vessel, thereby restoring blood flow. The major advantage of the mechanical thrombectomy device is it can expand the treatment windows from 3 hours to over 10 hours.
Some existing mechanical thrombectomy devices used for increasing blood flow through an obstructed blood vessel include: 1) a filter trap designed and built to collect and remove emboli; 2) a cork-screwed guidewire like device to retrieve embolus; and 3) a stent like device connected to a delivery wire to retrieve embolus. Filter thrombectomy devices suffer from the following disadvantages. The filters tend to be cumbersome and difficult to delivery, deploy and a larger profile guide catheter may be needed to fully remove the embolus. In addition, it is difficult to coordinate precisely and predictably a desired movement to position the device properly in the vessel. The device can drift within the vessel, twist, or not be adequately conforming to the vessel wall and, therefore not effective for removing embolus. Cork-screwed guidewire devices pose a disadvantage because they can only capture and remove emboli that are firm or subject to certain mechanical variables such as being held together by itself as one piece. Stent-like mechanical thrombectomy devices are not capable of capturing small emboli that break off from the large embolus if any, and can lead to complications such as blockage of distal smaller vessels, vessel dissection, perforation and hemorrhage arise as a result of over-manipulation in the vessel.
Disadvantages common to all of the devices described above include, for example: 1) the device may capture an embolus, but then lose grasp of it and migrate/deposit it incidentally in another area of the neurovasculature, creating the potential for a new stroke in a different part of the neurovasculature; 2) the device is not capable to capture the small embolus break off from the major embolus and prevent it from migrating to a more distal area of the neurovasculature; 3) the relative large device profile prevents it from treating the distal small diameter vessels.
Another disadvantage to existing mechanical thrombectomy devices is that they are built using two or more distinct pieces that require either joints or bonding between the delivery system and the treatment device. This connection of the pieces generally results in a weakness in the device that can result in an unintentional separation of the two pieces, possibly leaving the treatment device in the body during embolus retrieval. Also, the treatment portion of mechanical thrombectomy devices (particularly stent like devices) tend to be cut from tubing that is larger than the delivery system, thus making the treatment portion the limiting factor in terms of minimizing the compacted profile of the device, requiring larger access systems and greater delivery force to deliver the device.
Other flaws in the current mechanical thrombectomy designs include poor visibility/radiopacity, lack of variation in the delivery portion to enhance and improve deliverability, and lack of coatings or modified surface textures on the treatment portion to enhance embolus affinity, etc. In conclusion, there is a great need for improved devices, device systems, and methods for increasing blood flow through a blood vessel as described herein. None of the existing medical mechanical thrombectomy devices address all necessary needs to date.